Figure 48-10. External Real Time Oscillator with Load Capacitor
XOUT32
XIN32
32.768kHz
22pF
22pF
Table 48-6. External Real Time Oscillator Checklist
Signal Name
Recommended Pin Connection
Description
XIN32
Load capacitor 22pF
Timer oscillator input
XOUT32
Load capacitor 22pF
Timer oscillator output
1. These values are only given as typical examples.
2. The capacitors should be placed close to the device for each supply pin pair in the signal group.
Note:
In order to minimize the cycle-to-cycle jitter of the external oscillator, keep the neighboring pins as
steady as possible. For neighboring pin details, refer to the Oscillator Pinout section.
Related Links
on page 1169
48.6.4. Calculating the Correct Crystal Decoupling Capacitor
The model shown in
can be used to calculate correct load capacitor for a given crystal. This
model includes internal capacitors C
Ln
, external parasitic capacitance C
ELn
and external load capacitance
C
Pn
.
Figure 48-11. Crystal Circuit With Internal, External and Parasitic Capacitance
XOUT
Internal
C
EL1
C
L1
C
L2
C
P1
C
P2
C
EL2
External
XIN
Using this model the total capacitive load for the crystal can be calculated as shown in the equation
below:
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
1200